The precise position of approaching aircraft relative to the runway must be known to the pilot at all times and in all environmental conditions. Therefore, any readings received by the pilot from the equipment used for monitoring the position of his aircraft must be accurate, even in extreme weather conditions--severe thunderstorms, snow squalls, freezing rain, high winds, dense fog and the like. For the purposes of assisting the pilot, arrays of antennas are situated at for example, both ends of the runway, and over one of which arrays of antennas the aircraft must fly to reach the runway. In cases where false readings may be of concern (as for example, from vehicular traffic from a nearby highway) the arrays of antennas are associated with a reflecting screen. In Canada, Transport Canada has ordained that the situated arrays of antenna must not collapse, while withstanding 100 m.p.h. gusted wind, and carrying radial ice one inch in thickness, and must give accurate signals while withstanding 80 m.p.h. gusted wind, and carrying the same thickness radial ice. To achieve this end, the arrays of antenna (and reflecting screen, where necessary) are presently anchored in concrete pillars or posts, anchored into the ground. These posts are positioned at intervals of for example 239 cm. from their centre lines spanned by a bridge walkway for ready access to the antennas;
While the above structure fulfills Canadian Government Regulations, it also falls within the definition of a "fortress". Any aircraft inadvertently approaching the runway too low or, attempting to land short of the runway, will impact this fortress with such force that the aircraft will be torn apart with a high probability of loss of life;
It is therefore an object of this invention to provide a break-away structure, as for example, an ILS supporting bridge, employing frangibly connected joints being capable of failing in three modes--shear, tension and compression--to thereby reduce the destruction of any body impacting the break-away structure whereby the frangible joints receiving forces transmitted thereto after impact by a moving body with the structure will fail partially or completely, and in the event of partial failure, will transmit the remaining forces to at least a second frangible joint for the failure thereof and the collapse of the structure into smaller sections.
It is a further object of this invention to provide break-away ILS supporting bridge structures employing frangible connections in their construction which structures are capable of providing the necessary support for arrays of antenna used for signalling incoming aircraft, and which structures not only comply with Governmental Regulations, but also reduce the damage caused any aircraft impacting same;
Further and other objects of the invention will be realized by those skilled in the art from the following summary of the invention and detailed description of preferred embodiments thereof;